The present invention is concerned with a method and apparatus for applying strips of one material to a web of second material and, more particularly, is concerned with a method and apparatus for applying elastic strips to a moving web of material. For example, the present invention has utility with respect to the application of elastic leg and/or waistband strips to a moving web of material which will be transversely cut into individual disposable diapers or other garments.
Generally, disposable diapers or the like are made with a fluid impervious backing sheet on which an absorbent sheet is (or individual absorbent pads are) positioned and covered by a liquid-pervious top sheet. The composite material is then cut into individual disposable diapers or the like. In the manufacture of such articles it is conventional practice to apply elastic strips to a moving web of backing sheet material to provide elastic sealing about the leg openings of the finished garment. In modern manufacturing of disposable diapers, the web or webs of material from which the diapers are made move at high speeds and consequently the accurate application of elastic strips of desired configuration to the rapidly moving web presents significant manufacturing problems. These problems are intensified when it is desired to apply the elastic strips in other than a straight linear configuration.
U.S. Pat. No. 4,227,952 is illustrative of the prior art expedient of forming transverse folds or tucks at spaced locations along the web of material and applying, by means of adhesive, a stretched elastic ribbon or strip longitudinally of the web and extending over the transverse tucks or folds. The elastic ribbon or strip is maintained in stretched condition until the adhesive sets and is then severed at the point where the elastic ribbon crosses the folds so that upon longitudinally straightening the web to remove the folds, spaced apart segments of elastic ribbon are formed thereon.
U.S. Pat. No. 4,284,454 illustrates a method and apparatus for applying elastic ribbon or strips transversely of a moving web of material by utilizing a first chain conveyor to position discrete elastic strips transversely of the moving web. A second set of transfer chains moving parallel to and in the same direction as the traveling web are used to pick up the discrete strips of elastic and apply them in their transversely oriented position to the moving web of material.
U.S. Pat. No. 4,297,157 discloses an applicator for placing elastic strips longitudinally on a moving web of material, the applicator comprising a series of movable and fixed clamps mounted on a main rotor body by means of radially extending connecting rods. The applicator receives a continuous strip or ribbon of elastic and cuts it into discrete lengths for longitudinal application of discrete linear strips of the elastic to the moving web of material.
U.S. Pat. No. 4,293,367 discloses means whereby strips of elastic may be applied to a moving web of material in a gently undulating pattern comprising straight, longitudinally extending segments and gently curved curvilinear segments. This is attained by utilizing an applicator head (illustrated in FIG. 5 of the patent) which is reciprocated transversely relative to the moving web of material and simultaneously pivoted. The reciprocating movement applies the strips in the undulating pattern and the pivoting maintains the axes of the elastic strip applicator rolls perpendicular to the line of deposition of the elastic strip during both the linear and curvilinear portions of the application cycle.
U.S. Pat. No. 3,728,191 shows a device for applying waistband tape to disposable diaper material in which applicators for the tape are mounted on a rotatable member and are radially pivotable to selectively orient the applied tape to the moving web as illustrated in FIG. 5 and described at column 5, lines 57 et seq. of the patent. The applicators are brought into contact with the moving web of material by the eccentric cam track arrangement illustrated in FIG. 5.
As mentioned above, the high linear speed of the moving web or webs of material used in modern manufacturing techniques increases the difficulty of oscillating or undulating the applied elastic web rapidly enough to attain sharp curvatures of the applied strip relative to the high speed moving web. In addition to requiring extremely high speeds of oscillation or rotation of the applicator heads, high mechanical stresses are set up in the moving web of material by such sharp direction changes of the applied strips. The web material, which is usually quite thin and of limited mechanical strength, may not be able to withstand such stresses without tearing.